export default class Base64Util {
    // private property
    private static _keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='

    /**
     * 加密字符串为base64
     * @param input
     * @returns
     */
    static encode = (input) => {
        let output = ''
        let chr1, chr2, chr3, enc1, enc2, enc3, enc4
        let i = 0
        input = Base64Util._utf8_encode(input)
        while (i < input.length) {
            chr1 = input.charCodeAt(i++)
            chr2 = input.charCodeAt(i++)
            chr3 = input.charCodeAt(i++)
            enc1 = chr1 >> 2
            enc2 = ((chr1 & 3) << 4) | (chr2 >> 4)
            enc3 = ((chr2 & 15) << 2) | (chr3 >> 6)
            enc4 = chr3 & 63
            if (isNaN(chr2)) {
                enc3 = enc4 = 64
            } else if (isNaN(chr3)) {
                enc4 = 64
            }
            output =
                output +
                Base64Util._keyStr.charAt(enc1) +
                Base64Util._keyStr.charAt(enc2) +
                Base64Util._keyStr.charAt(enc3) +
                Base64Util._keyStr.charAt(enc4)
        }
        return output
    }

    /**
     * 解密base64为字符串
     * @param input
     * @returns
     */
    static decode = (input) => {
        let output = ''
        let chr1, chr2, chr3
        let enc1, enc2, enc3, enc4
        let i = 0
        input = input.replace(/[^A-Za-z0-9\+\/\=]/g, '')
        while (i < input.length) {
            enc1 = Base64Util._keyStr.indexOf(input.charAt(i++))
            enc2 = Base64Util._keyStr.indexOf(input.charAt(i++))
            enc3 = Base64Util._keyStr.indexOf(input.charAt(i++))
            enc4 = Base64Util._keyStr.indexOf(input.charAt(i++))
            chr1 = (enc1 << 2) | (enc2 >> 4)
            chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
            chr3 = ((enc3 & 3) << 6) | enc4
            output = output + String.fromCharCode(chr1)
            if (enc3 != 64) {
                output = output + String.fromCharCode(chr2)
            }
            if (enc4 != 64) {
                output = output + String.fromCharCode(chr3)
            }
        }
        output = Base64Util._utf8_decode(output)
        return output
    }

    // private method for UTF-8 encoding
    private static _utf8_encode = (string) => {
        string = string.replace(/\r\n/g, '\n')
        let utftext = ''
        for (let n = 0; n < string.length; n++) {
            let c = string.charCodeAt(n)
            if (c < 128) {
                utftext += String.fromCharCode(c)
            } else if (c > 127 && c < 2048) {
                utftext += String.fromCharCode((c >> 6) | 192)
                utftext += String.fromCharCode((c & 63) | 128)
            } else {
                utftext += String.fromCharCode((c >> 12) | 224)
                utftext += String.fromCharCode(((c >> 6) & 63) | 128)
                utftext += String.fromCharCode((c & 63) | 128)
            }
        }
        return utftext
    }

    // private method for UTF-8 decoding
    private static _utf8_decode = (utftext) => {
        let string = ''
        let i = 0,
            c = 0,
            c1 = 0,
            c2 = 0
        while (i < utftext.length) {
            c = utftext.charCodeAt(i)
            if (c < 128) {
                string += String.fromCharCode(c)
                i++
            } else if (c > 191 && c < 224) {
                c2 = utftext.charCodeAt(i + 1)
                string += String.fromCharCode(((c & 31) << 6) | (c2 & 63))
                i += 2
            } else {
                c2 = utftext.charCodeAt(i + 1)
                let c3 = utftext.charCodeAt(i + 2)
                string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63))
                i += 3
            }
        }
        return string
    }
}
